The field of satellite reception installations has seen an upsurge over the last few years. The services offered by such installations, in particular satellite television, have greatly contributed to this considerable development. In parallel with this, the market for video appliances of all kinds (TV, digital video recorder, and more.) has expanded significantly. Today, many households have a satellite reception installation comprising several processing units, or box, distributed within various rooms of the family home. In a typical installation all the processing units are connected to a single reception head, also referred to as an LNB (standing for “Low Noise Block downconverter”) or more simply designated by the term satellite receiver in the present description.
FIG. 1A illustrates the configuration of an installation of a residential installation comprising three processing units 213, 214, and 215. An initial satellite signal 1 is reflected and focused by a parabolic antenna 2 so as to be redirected towards a receiver 3. Output ports 4, 5 and 6 of the receiver are connected respectively to the processing units 213, 214, and 215 via coaxial cables 216, 217, and 218. The receiver 3 first carries out a selection of a signal from amongst several signals included in the initial signal, before carrying out a preprocessing on each signal selected. The preprocessed signals are then switched by a switching matrix so as to be transmitted via the coaxial cables 216, 217, and 218 to the respective processing units 213, 214, and 215. The term “signal” refers to an RF signal in the present description.
The basic principles of satellite reception, based on the functions of a conventional receiver, are described in greater detail hereinbelow.
One of the first functions of the receiver 3 is to collect the satellite signals. A satellite signal is generally broadcast according to two crossed polarizations, the two polarizations possibly being linear, that is to say horizontal and vertical, or else circular, that is to say left and right. Accordingly, a conventional receiver generally comprises two antennas. A first antenna for collecting the signals of horizontal, i.e., left polarization and a second antenna for collecting the signals of vertical, i.e., right polarization. The receiver carries out a first selection from among a first signal of horizontal polarization and a second signal of vertical polarization. Thereafter, the receiver amplifies the signal thus selected with the smallest possible noise factor.
Another important function of such a receiver is to lower the frequency band of the signal selected into a frequency band, commonly referred to as the transmission frequency band or else the Satellite Intermediate Band or SIB, compatible with the operation of the processing units. Typically, the satellite signal 1 is received by the receiver 3 in an initial frequency band lying between 10.7 GHz and 12.75 GHz. This frequency band is too high to be transmitted directly to a processing unit. It is therefore lowered by the receiver 3 in the SIB compatible with the capabilities of the processing units. Conventionally, the SIB lies between around 950 MHz and around 2150 MHz. The SIB may also lie between around 950 MHz and around 1450 MHz. A satellite signal with linear polarization and an SIB lying between 950 MHz and 2150 MHz are taken by way of example in the subsequent description.
The initial frequency band being wider than the SIB, the initial frequency band is divided into two parts: a low initial frequency band and a high initial frequency band. Thus, the receiver carries out a second selection from among a modulated signal in the low frequency band and a modulated signal in the high band. Upon completion of this second selection, the receiver selects one from among the four signals emanating from the initial satellite signal. The spectrum of these four signals is represented diagrammatically in FIG. 1B, whereby convention, spectra of vertical or horizontal polarization are represented respectively below or above the frequency axis. One thus distinguishes between the modulated vertically polarized signal in the low initial frequency band VeBa, the modulated vertically polarized signal in the high initial frequency band VeHa, the modulated horizontally polarized signal in the low initial frequency band HoBa and the modulated horizontally polarized signal in the high initial frequency band HoHa.
The receiver carries out a preprocessing of the signal selected before switching it via a switching matrix. This preprocessing consists in mixing the frequency of the signal selected previously with a predetermined mixing frequency so as to obtain a preprocessed signal in the SIB. The predetermined mixing frequency generally used for processing the low initial frequency band is conventionally 9.75 GHz and that for processing the high initial frequency band is conventionally 10.6 GHz.
The receiver 3 therefore provides four signals, emanating respectively from preprocessed signals VeBa, VeHa, HoBa and HoHa, which are selectively transposed into the SIB. FIG. 1B illustrates the four signals VeBa, VeHa, HoBa and HoHa referenced 201, 202, 203 and 204 respectively and which are included in the satellite external initial signal.
The coaxial cables referenced 216, 217 and 218 each transport at most one of the preprocessed signals described above, the same signal possibly of course being transported on several cables. Within the receiver, a microcontroller manages a switching matrix on the basis of commands received from the processing units so as to transmit a determined preprocessed signal to at least one respective processing unit. In general, such a switching matrix is integrated into the receiver. However, in certain installations the switching matrix forms part of another box connected to the receiver.
Each processing unit is in charge of processing one or more “useful” signals extracted from the preprocessed signal transmitted by the coaxial cable linking it to the receiver 3. Typically, the expression “useful signal” designates a signal corresponding to a given satellite channel.
In a conventional architecture of a satellite reception installation, the processing units are independent of one another and do not exchange information with one another.
Now, the need is apparent for the processing units of one and the same installation to be able to exchange data in the SIB. Specifically, these processing units may offer various functions such as a function for recording digital data of video or film type on a mass storage medium, a function for reading data thus recorded, a function allowing them to be connected to the telephone network, a function for managing decoding entitlements, and more.
There are several known solutions to share and exchange data in the SIB among processing units in a given installation. One solution is to install a new wire link and hence a new coaxial cable. This solution although useful, must be balanced by the major drawbacks of the cost of installation, the cost of maintenance and the unattractive sight of the cabling.
Another solution is to transmit a signal from a processing unit to another processing unit by way of operations carried out by the microcontroller. Specifically, the microcontroller can receive the signal from a processing unit, store it so as to repeat it in order to transmit it via the cable corresponding to the destination processing unit. Only signals of low throughput, such as the messages of a protocol such as the protocol known by the trade mark DiSEqC, may be exchanged using this solution between the processing units, generally at the frequency of 22 KHz. This solution although useful, does not provide a throughput that is high enough to transmit a quantity of information that is required by applications such as the transmission of audio and video signals since the signal dispatched by one processing unit to another processing unit is first received, then decoded and finally stored by the microcontroller of the receiver before being repeated so as to be transmitted to the other processing unit.
Another solution is based on wireless transmission by integrating a transceiver into each processing unit. However, this solution has the drawback of the financial cost of the equipment. Moreover, the operator providing a satellite-based service wishes to limit the access to this service solely to the subscribers to this service, thereby requiring particularly expensive measures for precluding access to the service by any neighbors of the subscribers who are not themselves subscribers. Providing this security to restrict access is very expensive in the field of wireless transmission.
Accordingly, a need exists to overcome the drawbacks and problems of the prior art and to provide an inexpensive and easy way to implement a system, included in a satellite reception installation which would allow the processing units of one and the same installation to share functions.